Interface between Fastrack Supreme and PIC

Yes, that’s one way to look at it.

Another way is to remember that Wavecom products are DCEs - ie, “modems” - and TX is always an input to a DCE

See: viewtopic.php?f=53&t=3081&p=11355&hilit=RTS+CTS#p11355
And: viewtopic.php?f=37&t=2919&p=10657&hilit=input+dce#p10657

A further way to look at it is that “Tx” is the name of the signal - not the name of a pin;
then, clearly, the Tx signal must come out of the DTE and go in to the DCE

In other words, “Tx” means “the data to be transmitted over the link”

See: viewtopic.php?f=5&t=2997&p=11015&hilit=input+dce#p11015